1. Field of the Invention
The present invention relates to an instrument for measuring illumination levels, a method of measuring illumination, and an exposure apparatus, and relates in particular to an illuminance meter used to measure relative illumination levels in several exposure apparatuses, a method of using the illuminance meter and an exposure apparatus equipped with the illuminance meter. This application is based on Japanese Patent Application Nos. 10-74861 and 11-275379, and the contents of which are incorporated herein by reference.
2. Description of the Related Art
A projection exposure apparatus is used in manufacture of semiconductor devices and liquid crystal displays and others, to imprint a pattern prepared on a mask or reticle (referred to as masking below) on a photo-sensitive substrate base such as a semiconductor wafer or a transparent substrate plate coated with a photo-sensitive material. In plants producing semiconductor devices and liquid crystal devices, projection exposure apparatus is not used singly, but in general, a group of such projection exposure apparatuses are used concurrently.
In such a production plant, to minimize the variation in the quality of products produced in different exposure apparatuses, it is necessary to match the operating exposure levels in different exposure apparatuses. For this reason, an internal optical sensor is installed in each exposure apparatus to indirectly determine the operating level of illumination at the image plane, and based on the results of such measurements, exposure levels of different apparatuses are matched accordingly. However, it is not guaranteed that each internal optical sensor provided in each apparatus always produce correct levels of illumination, because of chronological changes and other transitory factors that occur during the production process, so that the internal sensors must always be calibrated and adjusted accordingly.
Also, it is necessary to intensively control relative levels of illumination in order to match the productivity of exposure processing achieved in each apparatus.
Therefore, an illuminance meter is used to measure the relative illumination levels of different exposure apparatuses. The meter is detachable from an adapter section provided in the vicinity of a wafer holder disposed on the wafer stage so that an operator inserts the meter manually in the adapter to measure illuminance at the image plane. After completing illuminance measurements on one exposure apparatus, the operator repeats the same process successively on other exposure apparatuses to complete the task of determining the relative illumination levels.
However, because other parts of the projection optical system are also located in the vicinity of the wafer stage, it is necessary for the operator to attach and detach the illuminance meter by inserting an arm through a very limited space, and also, because the wafer stage is located some distance away from the operator, such a process is not easily carried out and is time-consuming, and furthermore, there is always a danger that the operator""s arm may brush against the wafer stage or other precision instruments located nearby, resulting in damaging or contaminating the system with dust particles to affect the performance of the projection optical system.
Another problem associated with such a process of illuminance measurement is that the work is sometimes carried out by interrupting the on-going exposure process, but attaching/detaching actions cause temperature disturbance inside the projection chamber housing of the exposure apparatus due to opening/closing of chamber door and other factors. It takes a long time for the chamber temperature to stabilize after the completion of a measuring task, and the exposure process cannot be resumed during this period.
It is, therefore, an object of the present invention to simplify the task of illuminance measurement of the illumination light in a projection optical system in an exposure apparatus, and to shorten the time required to perform such illuminance measurements.
The present invention is explained in the following by affixing reference numerals to various elements illustrated in the drawings, but the present invention is not limited to those parts illustrated in the drawings with reference numerals.
The present illuminance meter (50) determines a level of illuminance of a radiation in the vicinity of the image plane of an exposure apparatus used to exposure a pattern fabricated on a masking (11) onto a photo-sensitive substrate base (14) retained on a wafer stage (28) through an optical projection system (13) of the exposure apparatus, and a feature of the present invention is that an optical sensor (illuminance determination section 52) is provided in an instrument plate (dummy wafer 51), which is made as a thin disk so that the meter can be transported in a manner similar to the photo-sensitive base (14).
Because the illuminance meter is made into a thin disk form, it can be handled in a manner similar to regular photo-sensitive substrate bases, and be transported using the transport system (103) for the bases to be loaded/retained on the substrate stage to perform the task of illuminance measurements in the as-loaded condition, and after the task is completed, the base can be transported from the exposure apparatus to other processing stations.
Therefore, there is no need to mount/dismount the substrate base from the substrate stage as in the conventional technique, resulting in a simplified process of illuminance measurements. Also, there is no need for opening/closing the door to the controlled environment chamber so that the waiting time for the environment to return to normal is not necessary and measurements can be performed quickly, and therefore, the present illuminance meter enables to minimize interruptions caused by the task of illuminance measurements and to perform such measurements very efficiency.
The present method of determining a level of illuminance is based on using an illuminance meter (50) having an instrument plate (dummy wafer 51) formed with an optical sensor (illuminance determination section 52), and a feature that the instrument plate is made as a thin disk so that the meter (50) can be transported in a manner similar to regular photosensitive bases (14), to be loaded/unloaded onto/from a wafer stage (28) of a plurality of exposure apparatuses (30a, 30b, 30c, 30d) to determine an individual level of illuminance in the vicinity of the image plane of the optical projection system (13) of each exposure apparatus.
In the present method, because the illuminance meter is made in a form of a thin disk that can be transported in a manner similar to regular photo-sensitive substrate bases and illuminance measurements are made by loading and unloading the illuminance meter to the substrate stage in a manner similar to regular photo-sensitive bases to determine illuminance of each exposure apparatus, there is no need to mount and dismount an illuminance meter on and off the substrate stage as in the conventional technique, thus greatly simplifying the task of illuminance measurements.
Also, because there is no need for opening/closing the door to the controlled environment chamber so that the waiting time for the environment to return to normal is not necessary and measurements can be performed quickly, so that measurements of illuminance, in a production line that has a plurality of exposure apparatuses for making semiconductor devices based on photolithography, can also be performed quickly and management of each exposure apparatus is facilitated.
The present exposure apparatus performs exposure of a pattern fabricated on a making (11) on a photo-sensitive substrate base (14) held on a substrate holder (dummy holder 151) that is retained on a wafer stage (28) through an optical projection system (13) of an exposure apparatus, and a feature is that substrate holder can be freely attached/detached on/off the substrate stage, and an optical sensor (52) is provided on a holding surface of the substrate holder for holding the photo-sensitive substrate base.
Because the exposure apparatus has a substrate holder that can be freely attached to or detached from the substrate stage, and has the illuminance detection section therein, the substrate holder can be transported using the transport system (103) to load/unload the substrate holder on/off the substrate stage and to perform measurements in the as-loaded condition, and after the task is completed, the substrate holder can be transported from the substrate stage. Therefore, there is no need to mount/dismount the substrate base on/off the substrate stage as in the conventional technique, resulting in a simplified process of illuminance measurements. Also, there is no need for opening/closing the door to the controlled environment chamber so that the waiting time for the environment to return to normal is not necessary and measurements can be performed quickly, and therefore, the present illuminance meter enables to minimize interruptions cause by illuminance determination and to perform illuminance measurements very efficiency.
Further, a feature in the present method of illuminance measurements is that it is based on the use of a substrate holder (dummy holder 151) that can be freely attached/detached from the substrate stage (28) and has an integral optical sensor (52), so that the task of illuminance measurements can be performed by loading/unloading the substrate holder on the substrate stage to successively determine individual levels of illuminance in the vicinity of the image plane of the optical projection system for each exposure apparatus (30a, 30b, 30c, 30d).
Because the present method of illuminance measurements is based on a substrate holder, having the illuminance detection section integrated therein, that can be freely attached to or detached from the substrate stage, and illuminance measurements can be taken by loading/unloading the substrate holder on/off the substrate stage, there is no need to mount/dismount the substrate base from the substrate stage as in the conventional technique, resulting in a simplified process of illuminance measurements.
Also, because there is no need for opening/closing the door to the controlled environment chamber so that the waiting time for the environment to return to normal is not necessary and measurements can be performed quickly, so that measurements of illuminance, in a production line that has a plurality of exposure apparatuses for making semiconductor devices based on photolithography, can also be performed quickly and management of each exposure apparatus is facilitated.